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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO{sub 2}, anatase-TiO{sub 2} and Al{sub 2}TiO{sub 5}. PEO/α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) composite coating only had small micropores and appeared some α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) phase. Besides, the addition of α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation of Mixed-Type Craters and the Role of Bifluoride Additives to Produce Zirconia-Toughened Alumina-Based PEO Coating

Al{sub 2}O{sub 3}-ZrO{sub 2} composite ceramic coatings were prepared on Al6061 aluminum alloy by plasma electrolytic oxidation in Na{sub 3}PO{sub 4}-K{sub 2}ZrF{sub 6}-Na{sub 2}SiF{sub 6}-based alkaline electrolyte. Optimum processing time for the coating formation was found to be ~ 50 min. Cross section and surface morphology of the coatings were analyzed using scanning electron microscope. From the phase and elemental composition analysis, the presence of m-ZrO{sub 2} and t-ZrO{sub 2} phases was confirmed. It was further observed that the peak intensities of t-ZrO{sub 2} and α-Al{sub 2}O{sub 3} phases increased with processing time, which was attributed to the enhanced crystallinity caused by the efficient sintering conditions. Corrosion properties were investigated by potentiodynamic polarization test in 3.5 wt.% NaCl solution. The results showed high improvement in corrosion rate with minimum recorded value ~ 0.25 mmy (mm/year) and corrosion current ~ 0.15 × 10{sup −6} A/cm{sup 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Silicate Concentration in Electrolyte on the Growth and Performance of Plasma Electrolytic Oxidation Coatings Prepared on Low Carbon Steel

Plasma electrolytic oxidation (PEO) coatings were prepared on low carbon steel from electrolytes with different silicate concentrations. The microstructure, elemental and phase compositions of the PEO coatings were analyzed by scanning electron microscope, energy-dispersive spectrometer, and x-ray diffraction, respectively. The adhesion of PEO coatings with low carbon steel substrate was qualitatively examined by thermal shock tests. The tribological properties were evaluated by a reciprocating tribometer sliding against a Si{sub 3}N{sub 4} ceramic ball. The corrosion behaviors of PEO coatings were investigated in 3.5 wt.% NaCl solution by electrochemical impedance spectra and potentiodynamic polarization. Results indicated that all the PEO coatings were comprised of amorphous SiO{sub 2} and Fe-containing oxides; however, the silicate concentration in electrolyte showed significant influence on the growth and the performance of PEO coatings. The PEO coating prepared from the electrolyte with silicate concentration of 30 g/L had the highest Fe content because the substrate was more readily oxidized and showed a dense structure, resulting in the best comprehensive performance of adhesion, wear resistance, and corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tribological and Corrosion Properties of Coatings Produced by Plasma Electrolytic Oxidation on the ZA27 Alloy

In this paper, a continuous and dense coating was deposited on samples of the ZA27 alloy through the plasma electrolytic oxidation (PEO) process to improve its wear and corrosion performance. A nontoxic and environmentally friendly inorganic salt, Na{sub 2}SiO{sub 3}, is chosen as electrolytes with different concentrations. The effect of the concentration of Na{sub 2}SiO{sub 3} aqueous solutions on the coating performances was investigated. The coatings with 3Al{sub 2}O{sub 3}·2SiO{sub 2} (mullite), Zn{sub 2}SiO{sub 4} and Al{sub 2}O{sub 3} (either crystal phase or with some amorphous SiO{sub 2} phases) were formed by the PEO processes. It was found that the coating thickness increased with the increase in electrolyte concentration. However, the wear and corrosion resistance performance of the coatings did not improve as the coating’s thickness increased. This was due to the fact that the coating produced with electrolytes of 10 g/L has a porous structure with large pore size. Among all the samples, coating produced by 15 g/L Na{sub 2}SiO{sub 3} has the best wear and corrosion resistance, which is attributed to its continuous and dense structure with thickness of about 47 μm.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Electrochemical Corrosion Behavior of Plasma Electrolytic Oxidation Coatings Fabricated on Aluminum in Silicate Electrolyte

Plasma electrolytic oxidation (PEO) coatings were fabricated on the aluminum in silicate electrolyte. Microstructures and elemental compositions of these PEO coatings were examined by scanning electron microscopy (SEM) equipped with an energy-dispersive x-ray spectroscopy (EDS). Corrosion resistances of the coated samples were evaluated using the measurements of open-circuit potential (OCP), repetitive polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The results indicated that the PEO coatings not only act as a physical shield limiting the penetration of corrosive solution, but also establish an anodic location with high concentration of H{sup +} ions and other product ions as pitting corrosion begins. With the development of pitting corrosion, the accumulation of corrosion products inside the pits and pores of the coatings decreases the corrosion process effectively.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Improved Electrochemical Performance of Plasma Electrolytic Oxidation Coating on Titanium in Simulated Body Fluid

The effect of plasma electrolytic oxidation (PEO) pre-treatments on corrosion behavior of titanium in simulated body fluid (SBF) is investigated. Three pre-treatments are compared, using silicate, calcium phosphate and mixed silicate and calcium phosphate (1:1) electrolytes, respectively. The resultant coatings in different compositions and morphologies were examined by high-resolution field emission scanning electron microscopy equipped with energy-dispersive spectrometer and x-ray diffraction. The PEO-treated specimens revealed distribution of coating species, mainly the titanium-rich inner coating region. However, findings show highly localized variations in composition within their crystalline structures, due to the melting and rapid solidification of the coating material in three different electrolytes. Corrosion behavior of the coatings was also examined in SBF at 37 °C by potentiodynamic polarization, revealing an improvement in corrosion resistance for mixed electrolyte compared to silicate and calcium phosphate electrolytes.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A comparative study on CdS: PEO and CdS: PMMA nanocomposite solid films

Cadmium Sulphide (CdS) nanoparticles were reinforced in Poly(ethylene Oxide) (PEO) and Poly(methyl methacrylate) (PMMA) matrices by in situ technique. The presence of CdS in PEO and PMMA matrix was confirmed using X-ray photoelectron spectroscopy (XPS). Fourier Transform Infrared spectroscopy (FTIR) analysis disclosed the co-ordination of CdS in the matrices. Thermal analysis of the nanocomposites was carried out using Differential Scanning calorimetric studies (DSC). The optical studies using UV–vis spectroscopy were carried out to find the band gap of the materials and the absorption onset. The CdS particle size in the matrices was found by Effective Mass Approximation (EMA) model using the band gap values and was confirmed by TEM studies. The surface trapped emissions of the nanocomposites were observed from the photoluminescence (PL) spectra. The distribution of CdS particles in the polymer matrices were presented by Atomic force microscopic studies (AFM).

36 MATERIALS SCIENCE↗
DOE OSTI2016

Role of salt concentration in blend polymer for energy storage conversion devices

Solid Polymer Electrolytes (SPE) are materials of considerable interest worldwide, which serves dual purpose of electrolyte and separator between electrode compartments in renewable energy conversion/storage devices such as; high energy density batteries, electrochromic display devices, and supercapacitors. Polymer blend electrolytes are prepared for various concentration of salt (Ö/Li) with the constant ratio (0.5 gm) of each PEO and PAN polymers (blend polymer) using solution casting technique. Solid polymeric ionic conductor as a separator is the ultimate substitute to eliminate the drawback related to liquid and gel polymer ionic conductors. In the present work, solid polymer electrolyte film consisting of PEO, PAN and LiPF{sub 6} are examined for various concentration of lithium salt by keeping PEO/PAN blend ratio as a constant with a view to optimize the dominant salt concentration which could give the maximum conductivity at ambient temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Composite polymer electrolyte based on PEO/Pvdf-HFP with MWCNT for lithium battery applications

In the present study PEO and PVdF-HFP blend based composite polymer electrolytes (CPEs) has been prepared by using Multi Walled Carbon Nanotube (MWCNT), in order to examine the filler addition effect on the electrochemical properties. The complexed nanocomposite polymer electrolytes were obtained in the form of dimensionally stable and free standing films by using solution casting technique. The electrochemical properties of CPEs were measured by the AC impedance method. From the ionic conductivity results, the CPE containing MWCNT 2wt% showed the highest ionic conductivity with an excellent thermal stability at room temperature. The dielectric loss curve s for the sample 6.25wt% PEO: 18.75 wt% PVdF-HFP: 2wt% MWCNT reveal the low frequency β relaxation peak pronounced at high temperature, and it may caused by side group dipoles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Ion beam irradiation as a tool to improve the ionic conductivity in solid polymer electrolyte systems

Solid polymer electrolytes (SPEs) have potential applications in solid state electronic and energy devices. The optimum conductivity of SPEs required for such applications is about 10{sup −1} – 10{sup −3} Scm{sup −1}, which is hard to achieve in these systems. It is observed that ionic conductivity of SPEs continuously increase with increasing concentration of inorganic salt in the host polymer. However, there is a critical concentration of the salt beyond which the conductivity of SPEs decreases due to the formation of ion pairs. In the present study, solid polymer thin films based on poly (ethylene oxide) (PEO) complexed with NaBr salt with different concentrations have been prepared and the concentration at which ion pair formation occurs in PEO{sub x}NaBr is identified. The microstructure of the SPE with highest ionic conductivity is modified by irradiating it with low energy O{sup +1} ion (100 keV) of different fluencies. It is observed that the ionic conductivity of irradiated SPEs increases by one order in magnitude. The increase in ionic conductivity may be attributed to the enhanced segmental motion of the polymer chains due to radiation induced micro structural modification.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Temperature dependent dielectric properties and ion transportation in solid polymer electrolyte for lithium ion batteries

Solid polymer electrolyte (SPE) film consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend matrix with lithium tetrafluroborate (LiBF{sub 4}) as dopant ionic salt and poly(ethylene glycol) (PEG) as plasticizer has been prepared by solution casting method followed by melt pressing. Dielectric properties and ionic conductivity of the SPE film at different temperatures have been determined by dielectric relaxation spectroscopy. It has been observed that the dc ionic conductivity of the SPE film increases with increase of temperature and also the decrease of relaxation time. The temperature dependent relaxation time and ionic conductivity values of the electrolyte are governed by the Arrhenius relation. Correlation observed between dc conductivity and relaxation time confirms that ion transportation occurs with polymer chain segmental dynamics through hopping mechanism. The room temperature ionic conductivity is found to be 4 × 10{sup −6} S cm{sup −1} which suggests the suitability of the SPE film for rechargeable lithium batteries.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Controlling block copolymer phase behavior using ionic surfactant

The phase behavior of poly(ethylene oxide)-poly(propylene oxide-poly(ethylene oxide) PEO-PPO-PEO triblock copolymer [P85 (EO{sub 26}PO{sub 39}EO{sub 26})] in presence of anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solution as a function of temperature has been studied using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The measurements have been carried out for fixed concentrations (1 wt%) of block copolymer and surfactants. Each of the individual components (block copolymer and surfactant) and the nanoparticle–surfactant mixed system have been examined at varying temperature. The block copolymer P85 forms spherical micelles at room temperature whereas shows sphere-to-rod like micelle transition at higher temperatures. On the other hand, SDS surfactant forms ellipsoidal micelles over a wide temperature range. Interestingly, it is found that phase behavior of mixed micellar system (P85 + SDS) as a function of temperature is drastically different from that of P85, giving the control over the temperature-dependent phase behavior of block copolymers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Improved electrical properties of free standing blend polymer for renewable energy resources

Blend polymer electrolytes are prepared for salt concentration (Ö/Li = 4) with the constant ratio (0.5 gm) of PEO and PAN using solution casting technique. The prepared free standing solid polymeric film is characterized by Field Emission Scanning Electron Microscopy (FESEM) which confirms the homogeneous distribution of dissociated salt in blend polymer matrix. After addition of salt the ionic conductivity value is found to be of the order of 7.13 × 10{sup −5} Scm{sup −1} which is three orders higher when compared with pure blend polymer films. The microscopic interaction among the polymer-ion, ion-ion has been confirmed by the Fourier Transform Infrared (FTIR) Spectroscopy. A very fine correlation has been built in the electrical conductivity and FTIR result. On the basis of above finding, a prepared free standing solid polymeric film appears to be appropriate for the energy storage/conversion device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Electrode property of single-walled carbon nanotubes in all-solid-state lithium ion battery using polymer electrolyte

Electrode properties of single-walled carbon nanotubes (SWCNTs) in an all-solid-state lithium ion battery were investigated using poly-ethylene oxide (PEO) solid electrolyte. Charge-discharge curves of SWCNTs in the solid electrolyte cell were successfully observed. It was found that PEO electrolyte decomposes on the surface of SWCNTs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Novel nanorods based on PANI / PEO polymers using electrospinning method

In this work, we fabricated nanorods by applying an electric potential on poly (ethylene oxide) (PEO) and polyaniline (PANI) as a polymeric solution by electrospinning method. Testing was conducted on the samples by field emission scanning Electron microscope (FE-SEM), X-ray diffraction (XRD) and Photoluminescence. And the results showed the emergence of nanorods in the sample within glass substrate. Diameters of nanorods have ranged between (52.78-122.40)nm And a length of between (1.15 – 1.32)μm. The emergence of so the results are for the first time, never before was the fabrication of nanorods for polymers using the same method used in this research.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Atomistic simulation of graphene-based polymer nanocomposites

Polymer/graphene nanostructured systems are hybrid materials which have attracted great attention the last years both for scientific and technological reasons. In the present work atomistic Molecular Dynamics simulations are performed for the study of graphene-based polymer nanocomposites composed of pristine, hydrogenated and carboxylated graphene sheets dispersed in polar (PEO) and nonpolar (PE) short polymer matrices (i.e., matrices containing chains of low molecular weight). Our focus is twofold; the one is the study of the structural and dynamical properties of short polymer chains and the way that they are affected by functionalized graphene sheets while the other is the effect of the polymer matrices on the behavior of graphene sheets.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1993

Transient current interruption mechanism in a magnetically delayed vacuum switch

The capacity of a magnetically delayed vacuum switch to conduct current depends on the density of plasma injected into the switch. Exceeding the current capacity results in the switch entering a lossy mode of operation characterized by a transient interruption of the main current (opening behavior) and a rapid increase of voltage across the vacuum gap. Streak and framing photographs of the discharge indicate that a decrease of luminosity near the middle of the gap preceeds the transition to the opening phase. The zone of low luminosity propagates toward the cathode. This evidence suggests that the mechanism causing the opening phase is erosion of the background plasma in a manner similar to that in a plasma-opening switch. The resulting ion depletion forces a space-charge-limited conduction mode. The switch inductance maintains a high discharge current even during the space-charge-limited conduction phase, thus producing high internal fields. The high accelerating voltage, in turn, produces electron and ion beams that heat the electrode surfaces. As a result of the heating, jets of electrode vapor issue from the electrodes, either cathode or anode, depending on the selection of electrode materials.

Morris, Gibson, Jr.↗
NASA NTRS2014

5.8kV SiC PiN Diode for Switching of High-Efficiency Inductive Pulsed Plasma Thruster Circuits

Inductive Pulsed Plasma Thruster (IPPT) pulse circuits, such as those needed to operate the Pulsed Inductive Thruster (PIT), are required to quickly switch capacitor banks operating at a period of μs while conducting current at levels on the order of at least 10 kA. [1,2] For all iterations of the PIT to date, spark gaps have been used to discharge the capacitor bank through an inductive coil. Recent availability of fast, high‐power solid state switching devices makes it possible to consider the use of semiconductor switches in modern IPPTs. In addition, novel pre‐ionization schemes have led to a reduction in discharge energy per pulse for electric thrusters of this type, relaxing the switching requirements for these thrusters. [3,4] Solid state switches offer the advantage of greater controllability and reliability, as well as decreased drive circuit dimensions and mass relative to spark gap switches. The use of solid state devices such as Integrated Gate Bipolar Transistors (IGBTs), Gate Turn‐off Thyristors (GTOs) and Silicon‐Controlled Rectifiers (SCRs) often involves the use of power diodes. These semiconductor devices may be connected antiparallel to the switch for protection from reverse current, or used to reduce power loss in a circuit by clamping off current ringing. In each case, higher circuit efficiency may be achieved by using a diode that is able to transition, or 'switch,' from the forward conducting state ('on' state) to the reverse blocking state ('off' state) in the shortest amount of time, thereby minimizing current ringing and switching losses. Silicon Carbide (SiC) PiN diodes offer significant advantages to conventional fast‐switching Silicon (Si) diodes for high power and fast switching applications. A wider band gap results in a breakdown voltage 10 times that of Si, so that a SiC device may have a thinner drift region for a given blocking voltage. [5] This leads to smaller, lighter devices for high voltage applications, as well as reduced forward conduction losses, faster reverse recovery time (faster turn‐off), and lower‐magnitude reverse recovery current. In addition, SiC devices have lower leakage current as compared to their Si counterparts, and a high thermal conductivity, potentially allowing the former to operate at higher temperatures with a smaller, lighter heatsink (or no heatsink at all).

Toftul, Alexandra↗